1. Field of Invention
The present invention relates to a method for making a reinforced thermoplastic part, a bumper beam, and a bumper comprising such a beam.
2. Description of Related Art
It is known that fastening elements need to be provided on a bumper beam to connect the beam to a stone deflector and to connect the beam to the vehicle chassis. When the beam is made of aluminum, these fastening elements must be joined.
It has already been proposed that a bumper beam be made of thermoplastic, possibly reinforced with fibers, so that not only can the weight of the beam be reduced but also the fastening elements can be cast into the beam, improving the economics of manufacturing and assembling fastening elements. However, despite the ribs with which they may be provided, these thermoplastic beams have the drawback of being insufficiently rigid.
To solve this rigidity problem, the idea was conceived of making a bumper beam of reinforced thermoplastic combined with one or more reinforcing sheets made of a woven or bonded fabric of reinforcing fibers, particularly glass, mixed with thermoplastic material, said thermoplastic being present in the form of fibers of thermoplastic materials such as the materials sold under the name "Twintex" by the Vetrotex Company or present in the form of impregnated reinforcing fibers as in the materials in the reinforced thermoplastic sheet (RTS) family. The reinforcing sheet is heated, then placed in a mold where it is overmolded by the thermoplastic material. It then matches the shape of the mold and, after removal, appears on one of the faces of the beam. The presence of the reinforcing sheet is very useful because it confers high rigidity on the beam. However, this reinforcing sheet occupies an entire face of the beam.
Despite its relative viscosity when hot, the reinforcing sheet has only limited deformability, which prevents it from penetrating into the ribs and deep, narrow cavities of the mold of the type used for making fastening elements. Thus, the ribs or fastening elements on the face of the beam occupied by the reinforcing sheet were no longer made by molding. While the absence of a rib on this face can be compensated more or less successfully by a slightly modified beam design, the absence of fastening elements molded together with the beam compels one to return to a traditional fastening system in which the elements are joined to the beam.